The unusual age-distribution of the disease produced by RS virus, and the severe response to infection in children vaccinated with an inactivated RS-virus vaccine make it important to determine whether the structure, overall strategy of replication or the assembly and maturation of RS virus have unique aspects that may contribute to its pathogenesis. We have purified respiratory syncytial virus, resolved its proteins into 6-8 polypeptides and sequentially separated these from the virion, making possible the first comparison between the structural polypeptides of the virus and their organization, with that of other RNA enveloped virus. With the exception of the differences in the molecular weights of the virion polypeptides, RS virus resembles the other paramyxoviruses. The largest viral glycoprotein, VGP1, was demonstrated in human cell lines infected with both the Long and N2 strains of RS virus and in the viruses produced by these cells. VGP1 was also demonstrated in the RS long infected monkey BSC-1, but not in RS N2 infected BSC-1 cells. Despite its absence in the cells, VGP1 was present in the RS N2 virus produced by BSC-1 cells. These results suggest that VGP1 is a viral coded protein. We have also continued our studies on the HeLa culture persistently infected with RS virus. No evidence was obtained for either interferon or defective interfering particles in this culture. It would appear that establishment of the culture involved the simultaneous selection of a RS virus variant with a longer growth cycle and lower yield than that of standard RS virus and a more resistant cell that can modulate the viral infection. For the coming year, we propose to continue our studies of the polypeptides of the RS virus produced in cell lines of human, monkey and bovine origin and to initiate studies on the site and kinetics of synthesis of the virus glycoproteins in HeLa cells.